1. Field of the Invention
The present invention relates to a method for recording data in an optical recording medium, an apparatus for recording data in an optical recording medium and an optical recording medium and particularly, to a method for recording data in an optical recording medium and an apparatus for recording data in an optical recording medium which can record data in information recording layers other than an information recording layer farthest from a light incidence plane of an optical recording medium including a plurality of information recording layers in a desired manner and reproduce data from information recording layers other than the information recording layer farthest from the light incidence plane in a desired manner, and an optical recording medium which includes a plurality of information recording layers and can record data in information recording layers other than an information recording layer farthest from a light incidence plane thereof in a desired manner and reproduce data from information recording layers other than the information recording layer farthest from the light incidence plane in a desired manner.
2. Description of the Related Art
Optical recording media such as the CD, DVD and the like have been widely used as recording media for recording digital data. A need is felt for optical recording media of progressively larger data recording capacity and various proposals is made in order to increase data recording capacity of optical recording media.
This has led to the development of optical recording media having two recording layers and such optical recording media have already been put into practical use as the DVD-Video and the DVD-ROM and other optical recording media adapted to enable only data reading.
An optical recording medium adapted only for reading data and provided with two information recording layers is formed by laminating two substrates each having prepits constituting an information recording layer on the surface thereof, via an intermediate layer.
Further, an optical recording medium having two information recording layers has been recently proposed in connection with optical recording media in which data can be recorded by the user, namely, data rewritable type optical recording media (See Japanese Patent Application Laid Open No. 2001-243655 etc.).
In the optical recording medium disclosed in Japanese Patent Application Laid Open No. 2001-243655, each of the information recording layers is constituted by a phase change type recording film and dielectric films (protective films) formed so as to sandwich the phase change type recording film and the two information recording layers each having such configuration are laminated to each other via an intermediate layer.
In the case where data are to be recorded in an optical recording medium including a plurality of information recording layers in which data can be recorded by the user, a laser beam whose power is modulated to a recording power Pw higher than a reproducing power Pr is focused and projected onto one of the information recording layers and the phase of a recording film contained in the information recording layer irradiated with the laser beam is changed, thereby forming a recording mark in the recording film. Since the reflectivity of a region of the recording film in which the recording mark is formed is different from that of a blank region in which no recording mark is formed, data can be reproduced by projecting a laser beam whose power is set to the reproducing power Pr onto the recording layer and detecting an amount of the laser beam reflected from the recording film.
In the case where data are to be recorded in any one of information recording layers other than an information recording layer closest to a light incidence plane of an optical recording medium including a plurality of information recording layers in which data can be recorded by the user and data recorded in any one of the information recording layers other than the information recording layer closest to the light incidence plane are to be reproduced, a laser beam is projected onto the information recording layer via the information recording layers located closer to the light incidence plane with respect to the information recording layer. Therefore, in order to record data in any one of the information recording layers other than the information recording layer closest to the light incidence plane and reproduce data recorded in any one of the information recording layers other than the information recording layer closest to the light incidence plane in a desired manner, it is necessary for each of the information recording layers located closer to the light incidence plane than information recording layer concerned to have sufficiently high transmittance and it is accordingly usual for each of information layers other than the information recording layer farthest from the incidence plane to have no reflective film or to have only an extremely thin reflective film.
In this manner, in an optical recording medium including a plurality of information recording layers, since information recording layers other than the information recording layer farthest from the incidence plane usually have no reflective film or only an extremely thin reflective film, sufficient enhancement effect cannot be obtained in the information recording layers other than an information recording layer farthest from the incidence plane, unlike in the information recording layer farthest from the incidence plane, and a reproduced signal having a sufficiently high output (modulation) cannot be obtained therefrom.